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在催化过程中,直接化环旋的化
Stepan Chuprakov1, Michael Rubin, Vladimir Gevorgyan
1Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street Chicago, Illinois 60607-7061, USA.
Journal of the American Chemical Society
|March 18, 2005
概括
直接的催化使得四位置换环烯的高效合成成为可能,包括以前无法获得的非血形式. 这种Heck型转换为复杂的环烯衍生物提供了一条新的途径.
科学领域:
- 有机化学 有机化学
- 催化剂是一种催化剂.
- 合成方法论 合成方法论
背景情况:
- 环烯是具有独特反应性的压力循环碳化合物.
- 现有的合成替代环烯的方法,特别是不对称的方法,存在局限性.
- 催化交叉合反应是有机合成中的强大工具.
研究的目的:
- 开发一种用于循环烯的直接和异的新方法.
- 为了实现高位环烯的高效合成,包括位丰富的环烯.
- 探索这种转变的机械路径.
主要方法:
- 使用环基质的直接催化和异化反应.
- 采用各种化和化作为合伙伴.
- 进行机理学研究以阐明反应途径.
主要成果:
- 展示了第一例直接催化和环烯的异.
- 成功合成了多种四位置换环烯.
- 获得非血糖环烯,这些环烯无法通过当前的不对称环烯技术获得.
- 机械学研究表明,赫克类反应的特征是电友性路径.
结论:
- 已经建立了一个新的,高效的合成路径,以得到四位置换和非血性环烯.
- 开发的催化方法克服了现有的不对称环化策略的局限性.
- 转换通过一种电友,Heck型机制进行.
相关概念视频
02:50Catalysis
The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
01:27Catalysis
Catalysis influences the rate of chemical reactions by providing an alternative reaction pathway with lower activation energy. A catalyst speeds up a reaction, but it is not consumed during the process. The fundamental principle of catalysis is the ability of a catalyst to alter the reaction mechanism, often introducing a more efficient pathway than the uncatalyzed process.In a catalyzed reaction, the catalyst participates directly in the reaction mechanism. It interacts with reactants to form...
01:22Heterogeneous Catalysis
Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...